S ince 1962, architect Paul Rudolph of New Haven, Con- necticut, has been developing a technique for building in concrete which demonstrates a new means for achieving a beautiful concrete finish. In the Yale University Art and A rc h i t e c t u re building in New Haven, and in the Endo Laborato- ries building at Garden City, Long Island, Mr. Rudolph has built with a rough concrete surface. Rather than showing the wood texture of the concrete forms after they have been removed, this surface shows the beauty of the concrete itself. Mr. Rudolph’s method invo l ve s the preparation of finned forms. On a plywood backing, trapezoidal fins 2 inches deep by 1 _ inches at the base by _ inch at the top are nailed in place. They form a regular pat- tern, the space between the fins be- ing equal to the width of the fins. These forms are placed as usual for any concrete wall. A stiff mixture of concrete with about a 2-inch slump and 1- to 1 1/2-inch aggre- gate is then placed. Cement, sand, and aggregate for the entire job are stock-piled before starting in order to assure consistency of surface tone. After removal of the forms, the fins are broken off with a hammer, thus exposing the aggregate. Often the aggregate breaks along with the concrete, and the interior tones of the aggregate are exposed. The stiff mixture avoids filming over aggregate stones which are not bro- ken. In this way, the building takes on the warm tone of the aggregate. This method does more than dec- orate an otherwise smooth concrete surface. Often used both inside and outside, it eliminates the necessity of any further finishing of the con- c re t e. In addition, the vertical fins suppress the subtle color changes visible in a smooth concrete surface. The finned method of concrete surface treatment was developed for the building at Yale, where Mr. Rudolph is chairman of the archi- tectural department. Se ve ral experi- ments were made before the suc- cessful method was found. One experiment involved backing the t ra p ezoidal elements with cross slats, in order to achieve the rough surface without the necessity of hammering. This method, however, was found to produce too weak a form when applied to the scale nec- essary in building. Therefore, the plywood backing was used. A large sample section was placed on the building site before the method was approved. Nearly all concrete surfaces in the Yale building are treated with the rough finned technique. The four hollow rectangular pillars which are the major structural elements rising inside the building are finished in this way. Those walls which are not glass are also treated with fins. Only parts of the basements and the sixth and seventh floors, where artists need tackable surfaces, are given a smooth finish. The Long Island laboratory differs from the Yale Art and Architecture building in two ways. First, the finned technique, used only on flat surfaces in New Haven, is applied to curved surfaces. In most places this is done without the necessity of curving the forms. The transitions between 1-foot flat segments set on a curve are easily obscured by the activity of the fluted surface. The ap- pearance is that of a true curve. A true curve was, in fact, used on the forms of only a small portion of the building. On the whole, the corduroy sur- face is used more sparingly at Endo. The only interiors finished with the rough surface are those of the tur- rets on the office wing and of the lobby. The remainder of the build- ing called for smooth interior finish, since it is to be used for laboratories. General contractor for Yale’s Art and Architecture building was the George B. H. Macomber Company. The aggregate for the Yale building was brought from Easton, Massa- chusetts. The Easton stone was cho- sen for its warm yellow and gold tones which would be exposed by the hammering. The aggregate for the Endo build- ing was a standard bank-run gra ve l from Long Island. This stone has a high percentage of light-colored quartz. All the concrete work on that building was done by the Ce n t ra l Cement Finishing Company of New York City. General contractors were Walter Kidde Constructors. Both jobs ran an average cost of $26.00 per square foot. The Rudolph treatment calls for one to two dol- lars more per square foot than a conventional concrete surface. This figure includes the extra one inch of width which must be allowed in the volume of concrete, and the cost of creating the fluted forms. The fluted technique, howe ve r, still under- prices many alter native surface treatments, since the final surface is built into the concrete walls. Paul Rudolph’s Fluted Concrete Buildings